Technical Field
The present invention relates to a touch detecting device and a semiconductor device that is applied thereto, and particularly, to a technology of adjusting offset of a detection target capacitor of a touch panel, for example, a technology that is effectively applied to a touch sense input system and the like of a personal digital assistant (PDA) or a tablet personal computer (PC).
Description of the Related Art
In a touch panel, which corresponds to multi-point touching by a mutual capacitance method, for example, Y electrodes as drive electrodes and X electrodes as detection electrodes are disposed to be perpendicular to each other with a dielectric interposed therebetween, and an intersection capacitor as a cross-coupling capacitor of respective intersecting portions constitutes an intersection capacitor. If a capacitance due to a finger or a hand is present in the vicinity of the intersection capacitor, the mutual capacitance of a corresponding node is reduced by a composite capacitance due to the finger or hand. To determine which capacitor a variation of the mutual capacitance occurs at, the touch panel controller sequentially drives the drive electrodes with a pulse to perform a charging operation of a pulse unit, sequentially repeats an operation of detecting a variation in electric charges, which are charged, from the respective detection electrodes, and allows a detection circuit to acquire a signal in accordance with a variation in the mutual capacitance of the intersection capacitors, which are arranged in a matrix shape. The controller, which drives the touch panel by using the mutual capacitance method to detect a signal, is disclosed, for example, in JP-A-2012-234473.
JP-A-2012-234473 gives attention to a configuration in which a parasitic capacitive component is present in a route ranging from the intersection capacitor to the detection circuit, and deviation is present in the size of the parasitic capacitance component in accordance with the position or layout of the X electrodes. This deviation appears as a deviation in an amount of electric charges that are input to the detection circuit through the X electrodes. Therefore, as a calibration technique of correcting an effect due to the deviation, JP-A-2012-234473 suggests a technology of performing offset adjustment in correspondence with each intersection capacitor. That is, a calibration circuit that performs offset adjustment with respect to input signals or output signals of a plurality of detection circuits corresponding to a plurality of X electrodes of the touch panel, and a memory that stores adjustment parameters of the calibration circuit are provided in the touch panel controller. According to this, it is possible to adjust a deviation in non-touching detection data with high accuracy for each of the intersection capacitors of the touch panel. Accordingly, a detection voltage detected by the detection circuit enters into an input range of an A/D converter.
In addition, JP-A-2012-234473 describes how to cope with a case where an optimal value of the adjustment parameters varies due to a variation in an environment (ambient temperature, humidity). That is, two RAMs that store an adjustment parameter are provided to cope with the environmental variation, and one RAM is rewritten with an adjustment parameter corresponding to the environmental variation while using an adjustment parameter stored in the other RAM. After the rewriting is completed, the RAM to be used is changed.